High-frequency amplifier, including a velocity modulation tube



April 3, 1951 M. J. o. STRUTT ET AL 2, 3

HIGH-FREQUENCY AMPLIFIER, INCLUDING A VELOCITY MODULATION TUBE Filed Feb. 15, 1947 fly:

L i -L L L l l MuLQSTRUTT a. A.VAN'DER 21a.

'INVENTORS AGENT Patented Apr. 3, 1951 "UNITED STATES PATENT OFFICE HIGH-FREQUENCY AMPLIFIER, INCLUDING A VELOCITY MODULATION TUBE Maximiliaan Julius Otto Strait and Aldert van der Ziel, Eindhoven, Netherlands, assignors to Hartford National Bank and Trust Company, Hartford, Conn, as trustee Application February 15,1947, Serial No. 728,800 In Belgium December 29, 1944 Section 1, Public Law 90, August 8, 1946 Patent expires December 29, 1964 claimed in specification of U. S. application Serial Number 683,704 filed July 15, 1946, now abandoned. In the said specification a circuit-arrangement for the transmission of ultra-highfrequency electric oscillations is described, which comprises at least one controlled discharge tube. According to the prior specification the circuit of a'control' electrode includes a resonant circuit which is tuned to a lower frequency than that of the oscillations to be transmitted and the impedan'ce and detuning of which are chosen to be such-that the'noise voltage which is produced across the resonant circuit by induction noise current flowing to the control electrode controls the output current of the tube in such phase and with such intensity that the noise current correlated with the said induction noise current in the output circuit is substantially suppressed. In the transmission of ultra-high frequency oscillations use may be made with advantage of a discharge tube in which an electron beam is produced, the velocity of which is controlled with the aid of a. velocity control electrode by the oscillations to be transmitted, after which the velocity variations of the beam are converted into intensity variations, the output voltage being obtained from these intensity variations. Such a -"discharge tube has the advantage that the dampi'ng exerted by the tube on the input impedance is'but low., It is, however, a disadvantage that owing to the great intensity of the cathodecurrent, the' cathode-noise is very strong. The use "of such a discharge tube in a receiver circuit is therefore only possible if use is made of means operative to reduce the noise.

-- Severalsuggestions have previously been made to compensate the noise ofdischarge tubes got the aforesaid type on the principle set out in the prior specification. According to one of these For this purpose the said control &.According to a further suggestion the input "resonant circuit included in the circuit of the velocity control electrode is tuned to a'low'er. fre- 'qn'ency than that ofthe oscillations-to be trans- 6 Claims. (Cl. 179 171) 2 mitted. In addition it has been suggested to arrange an auxiliary electrode between the electrode system for the generation of the electron beam and the velocity control electrode, said aux- 5 'iliary electrode also likewise controlling the velocity of the beam, and in this case to choose the impedance in the circuit of the auxiliary electrode and the input impedance included in the circuit of the velocity control electrode so far as the value and the phaseare concerned in such manner that the noise of the beam at the area of the output electrode is substantially suppressed. 7

The invention is based on the last mentioned 35 suggestion and has for its object to provide a circuit, in which a practically complete noise compensation is attended by a high gain.

According to the invention, solely the circuit of the auxiliary electrode includes a resonant circuit tuned to a lower frequency than that of the oscillations to be transmitted.

The input resonant circuit included in the circuit of the velocity control electrode is accurately tuned to the frequency of the oscillations to be transmitted in order to secure a maximum gain. Theoretical arguments revealed that it may be advantageous for the obtainment of a maximum signal noise ratio to tune the input resonant circuit to a higher frequency than that 30 of the oscillations to be transmitted.

The resonant circuit included in the circuit of the auxiliary electrode should preferably have a maximum impedance. The quality of this resonant circuit is therefore preferably chosen so as to le equal to or to exceed that of the input circui In order to reduce the induction noise current passing to the velocity control electrode as far as (possible, it is desirable that the electron beam should have a but small noise component at the area of the velocity control electrode. This can be ensured by choosing the spacing between the auxiliary electrode and the velocity control electrode comparatively large, to wit at least of the same order of magnitude as the spacing between the velocity control electrode and the output electrode.

In order that the invention may be clearly understood and readily carried into effect, it

will now be explainedmore fully with reference to the accompanying drawing, in which one construction is shown by way of example.

The single figureof the drawing shows a dis- 5c -for:thewgenerationiot an electron beam which comprises a cathode 2, a control electrode (Wehnelt cylinder) 3 and a pierced anode 4. The beam generated by this system passes successively through a plurality of hollow, cylindrical electrodes 5, 6, I, 8, 9, H and H and finally reaches a collecting electrode [2. in an aerial l3 are inductively transmitted to an input resonant circuit M which is included in the circuit of the electrode 8 which acts as a velocity control electrode. With the aid of the electrode 8 the velocity of the electrons of the beam is varied in synchronisrn with the signal oscillations.

The signal oscillations 4 ever, been found that a still greater signal noise ratio is obtainable in the output resonant circuit 15 by tuning the circuit [4 to a higher frequency than the signal frequency, so that the circuit [4 behaves as an inductance as far as the signal frequency is concerned.

What we claim is:

In the drift space enclosed by the electrodes the slow electrons are overtaken by the rapid electrons, with the result that successive maxima and minima of the electron density (intensity variations) occur. From these intensity variations the output electrode l6 obtains an output voltage which is set up across the output resonant circuit l5 and which is withdrawn via a pair of terminals 16 and i1. 1 v

The emission current of the cathode 2 is subjected to fluctuations, owing to which the beam of electrons exhibits intensity fluctuations which lead to a noise voltage across the output resonant circuit l5. According to the invention, this noise voltage is compensated in the following manner:

The electrode system 2, 3, d and the velocity control electrode 8 have arranged between them an auxiliary electrode 6, which also controls the velocity of the electrons of the beam. The circuit of this auxiliary electrode includes a resonant circuit i8 which is tuned to a lower frequency than-thatof-the incoming signal and which consequently behaves as a capacity so far as the signal frequency is concerned. As has been fully set out in the prior specification, the auxiliary electrode 6 has supplied to it an induction noise current which leads in phase by about 90 with respect to the intensity fluctuations of the beam at the area of the electrode This induction noise current brings about a noise voltage across the resonant circuit l8 which is in phase with the intensity fluctuations of the beam. This noise voltage controls the velocity of the electron beam and thus produces a noise component of the else-- tron beam at the area of the electrode 16, which assuming the impedance and the detuning of the resonant circuit is correctly proportioned is capable of substantially compensating for the remaining noise components so that a noise voltage does practically not occur across the output resonant circuit [5.

The impedance and detuning of the resonant circuit l8 should be a maximum to ensure corn piete compensation, to wit as high as and, if possible, higher than the impedance of the input r'esonant'circuit I4. I

Also the control electrode 8 has an induction noise current passing to it, which brings about a noise voltage across the circuit M which icontrols the velocity of the electron beam. It is desirable that this noise voltage should be kept low, as can be ensured by taking care that the electron beam at the area of the electrode 8 exhibits but comparatively small intensity fluctuations. For this purpose the distance between the electrodes 6 and 3 should be comparatively large, to Wit at least of the same order of magnitude as the distance between the electrodes 8 and ill; in this 'case'a partial noise compensation has already ensued at the area of the electrode 8.

In order to ensure a maximum amplification .the resonant circuit I4 is preferably tuned a'c- .curatehz.:tov the. signal frequency.- .,Itl1as,,how-

1. Apparatus for the amplification of high frequency oscillations comprising a velocity modulation tube including, in successive coaxial arrangement, an electrode system for generating an electron beam, a first cylindrical velocitycontrol electrode, a second cylindrical velocity- ,control electrode, a cylindrical drift space electrode, a cylindrical output electrode and a collecting electrode, a noise suppression resonant circuit, an input resonant circuit, an output resonant circuit, a source of accelerating potential for said tube, a positive terminal of said source being connected through said noise suppression circuit, said input circuit and said output circuit to said first control electrode, said second control electrode and said output electrode, respectively, and directly to said drift space electrode, and means to apply the oscillations to be amplified to said input circuit, said noise suppression circuit being tuned to a lower frequency than that of the oscillations to be transmitted.

2. Apparatus for the amplification of highfrequency oscillations comprising a velocity modulation tube including, in successive coaxial arrangement, an electrode system for generating an electron; beam, a first cylindrical velocity control electrode, a second cylindrical velocity control electrode, a cylindrical drift space electrode,

a cylindrical output electrode and a collecting electrode, a noise suppression resonant circuit, an input resonant circuit, an output resonant circuit,- a source of accelerating potential for said tube, a positive terminal of said source being frequency oscillations comprising a velocitymodulation tube including,.in successive coaxial arrangement, an electrode system for generating an electron beam, a first cylindrical velocity control electrode, a second cylindrical velocity control electrode, a cylindrical drift space electrode, a cylindrical output electrode and-a collecting electrode, a noise suppression resonant circuit, an input resonant circuit, an output resonant circuit, a source of accelerating potential for said tube, a positive terminal of said source being connected through said noisesuppression circuit, said input circuit and said output circuit to said first control electrode, said "second control electrode and said output electrode respectively, and directly to said drift space electrode, and means to apply the oscillations to be amplified to said input circuit-said: noise suppression circuit being tuned to a lower-frequency than that of the oscillations to be transmitted, said input circuit being tuned to a higher frequency than that of said oscillations.

4. Apparatus for the amplification of high frequency oscillations comprising a velocity modulation tube including, in successive coaxial arrangement, an electrode system for generating an electron beam, a first cylindrical velocity control electrode, a second cylindrical velocity control electrode, a cylindrical drift space electrode, a cylindrical output electrode and a collecting electrode, a noise suppression resonant circuit, an input resonant circuit, an output resonant circuit, a source of accelerating potential for said tube, a positive terminal of said source being connected through said noise suppression circuit, said input circuit and said output circuit to said first control electrode, said second control electrode and said output electrode respectively, and directly to said drift space electrode, and means to apply the oscillations to be amplified to said input circuit, said noise suppression circuit being tuned to a lower frequency than that of the oscillations to be transmitted, said input circuit being tuned to a higher frequency than that of said oscillations, said noise suppression circuit having a quality characteristic exceeding that of said in ut circuit.

5. Apparatus for the amplification of high frequency oscillations comprising a velocity modulation tube including, in successive coaxial arrangement, an electrode system for generating an electron beam, a first cylindrical velocity control electrode, a second cylindrical velocity control electrode, a cylindrical drift space electrode, a cylindrical output electrode and-a collecting electrode, the distance between said first and secand control electrodes being at least equal to the distance between the second control electrode and the output electrode, a noise suppression resonant circuit, an input resonant circuit, an output resonant circuit, a source of accelerating potential for said tube, a positive terminal of said source being connected through said noise suppression circuit, said input circuit and said output circuit to said first control electrode, said second control electrode and said output electrode respectively, and directly to said drift space electrode, and means to apply the oscillations to be amplified to said input circuit, said noise suppression circuit being tuned to a lower frequency than that of the oscillations to be transmitted.

6. Apparatus for the amplification of high frequency oscillations comprising a velocity modulation tube including, in successive coaxial arrangement, an electrode system for generating an electron beam, a first cylindrical velocity control electrode, a second cylindrical velocity control electrode, a cylindrical output electrode and a collecting electrode, the distance between said first and second control electrodes being at least equal to the distance between the second control electrode and the output electrode, a noise suppression resonant circuit, an input resonant circuit, an output resonant circuit, a source of accelerating potential for said tube, a positive terminal of said source being connected through said noise suppression circuit, said input circuit and said output circuit to said first control electrode, said second control electrode and said' output electrode respectively, and directly to said drift space electrode, and means to apply the oscillations to be amplified to said input circuit, said noise suppression circuit being tuned to a lower frequency than that of the oscillations to be transmitted, said input circuit being tuned to a higher frequency than that of said oscillations, said noise suppression circuit having a quality characteristic exceeding that of said input circuit.

MAXIMILIAAN JULIUS OTTO STRUTT. ALDERT VAN DER ZIEL.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 

